Sonic techniques and apparatus for stretch forming



Nov. 28, 1967 A. G. BODINE, JR 3,

SONIC TECHNIQUES AND APPARATUS FOR STRETCH FORMING Filed Jan. 18, 1965 5 Sheets-Sheet 1 Ila.

F, SIN wt FIG. la

FIG. lb

ATTORNEY ALBERT G. BODINE, R

Nov. 28, 1967 500mg, JR 3,354,688

SONIC TECHNIQUES AND APPARATUS FOR STRETCH FORMING Filed Jan. 18, 1965 5 Sheets-Sheet INVENTOR.

ALBERT G. BODINE, JR.

ATTORNEY NOV. 28, 1967 BODWE, JR 3,354,688

SONIC TECHNIQUES AND APPARATUS FOR STRETCH FORMING Filed Jan. 18, 1965 5 Sheets-Shee1 5 FIG. 4

INVENTOR ALBERT G. BODINE, JR.

ATTORNEY 1967 A. G. BODINE, JR 3,35

SONIC TECHNIQUES AND APPARATUS FOR STRETCH FORMING Filed Jan 18, 1965 5 Sheets-Sheet 4 FIG. 7a. ALBERT GRBODINE, JR.

ATTORFEY 1967 A. G. BODINE, JR 3,

SONIC TECHNIQUES AND APPARATUS FOR STRETCH FORMING Filed Jan. 18, 1965 5 Sheets-Sheet 5 75 INVENTOR.

FIG. 7b ALBERT e. BODINE, JR.

ATTORNEY United States Patent f 3,354,688 SONIC TECHNIQUES AND APPARATUS FOR STRETCH FORMING Albert G. Bodine, In, 7877 Wooziley Ave., Van Nuys, (Iaiif. 91466 Filed Jan. 18, 1965, Ser. No. 426,101 21 Claims. (Cl. 72297) ABSTRACT OF THE DISCLOSURE Method and apparatus for improved stretch forming of a member comprising utilizing sonic resonant vibration applied to the member.

This invention relates to sonic techniques and apparatus for stretch forming and more particularly to such devices and methods for facilitating and improving the shaping of metal structures by bending while simultaneously subjecting same to tension.

Metallic sheet or strip material can be formed to a desired shape by subjecting such material to tension by stretching and while under such tension shaping it on a tion between the material being shaped and the shaping form. Further, in stretch forming techniques of the prior art, a considerable amount of springback is encountered, making it necessary that the part be over-shaped in order to achieve the desired end results. Often too, a part stretch formed by techniques of the prior art will go out of shape due to some stress relieving influence like subsequent machining, welding, heating or even aging.

The method and devices of this invention overcome many of the above enumerated shortcomings of prior art stretch forming by effectively Working the material by sonic action while the stretch forming is being accomplished. By applying a sonic vibration to the material while it is being stretch formed, it has also been found that less force is needed for forming, the material forms easier and there is a very noticeable reduction in immediate springback so that very little over-shaping is required. Further, the sonic action stress relieves the material so that it will not go out of shape subsequently due to a later stress relieving influence. The sonic action also lessens the friction between the material being formed and the shaper, due both directly to the vibration itself at the contacting surfaces and the stress effects on the material which reduces the tensioning required, thus lessening the wear on the material in the forming process.

In achieving the desired end results, the devices and method of this invention typically utilize a mechanical oscillator which is connected to the mate-rial being formed to provide a sonic vibration therein. This mechanical oscillator is designed so that it has an output frequency at or near the resonant vibration frequency of the work piece or the associated stretching and holding assembly. The material is thus vibrated vigorously by means of the oscillator while it is being tensioned by the stretching mechanism.

Although the exact reasons why such sonic action has such marked effect in facilitating and improving stretch forming are not completely understood, it is believed that this is due to the fact that stress relief characteristics are 3,354,688 Patented Nov. 28, 1967 imparted to the material either by virtue of heating by hysteresis effect or by virtue of working or vibrational stressing of the material.

It is therefore an object of this invention to facilitate the stretch forming of metal objects.

It is a further object of this invention to provide improved methods and apparatus for stretch forming metal objects.

It is still another object of this invention to lessen the amount of tensioning necessary in stretch forming.

It is still a further object of this invention to minimize the wear and tear on material being stretch formed.

It is still another object of this invention to improve the shaping possible by means of stretch forming techniques.

It is still another object of this invention to minimize the amount of springback incidental to stretch formmg.

It is still a further object of this invention to stress relieve material while it is being stretch formed to minimize possibilities of shape loss due to subsequent stress relieving influences.

Other objects of this invention will become apparent from the following description taken in connection with the accompanying drawings, of which,

FIGS. 1a and 1b are schematic drawings illustrating the analogy between mechanical and electrical circuits,

FIG. 2 is a side elevation view of a first embodiment of the device of the invention,

FIG. 3 is a cross-sectional view taken along the plane indicated by line 36 in FIG. 2,

FIG. 4 is an end elevation view of the embodiment of FIG. 2,

FIG. 5 is an elevation cross-sectional view of an oscillator mechanism that may be utilized with the device of the invention,

FIG. 6 is a cross-sectional view of the oscillator shown in FIG. 5 as taken along the plane indicated by the line 6-6 in FIG. 5,

FIG. 7a is an elevation view partially in cross-section of a second embodiment of the device of the invention in a first operating position, and

FIG. 7b is an elevation view of the second embodiment of the device of the invention in a second operating position.

In order to facilitate the comprehension of the principles of sonics, a dynamic analogy between a mechanical vibrating circuit and an electrical circuit excited by an alternating current is often made. This type of analogy is well known in the art and is described for example in Dynamical Analogies, by Harry F. Olson, published in 1943 by D. Van Nostrand Company, New York, and in chapter 2 of Sonics by Hueter and Bolt, published in 1955 by John Wiley and Sons. Such an analogy is illustrated in FIGS. 1a and 1b, with FIG. 1a showing the mechanical equivalent for the electrical circuit shown in FIG. lb. Thus, in FIG. 1a, F sin t represents the vibrating driving force which is equivalent to electrical drive signal E sin wt of FIG. 1b. Similar-1y, the compliance of the circuit C represented for convenience by spring 11a in FIG. la, is equivalent to the capacitance C in the electrical circuit 1]), represented by capacitor 11b; also, the resistance R in the circuit 1a represented by dashpot 12a is equivalent to the resistance R represented by resistor 12b in FIG. 1b; and the mass M represented by block 13d in FIG. 1a is equivalent to the inductance of the circuit of FIG. 1b represented by inductor 13b. It is to be kept in mind that circuit parameters C R and M of FIG. la, and C R and L of FIG. 1b are not generally lumped in the circuit but are distributed throughout the components thereof, and are schematically illus- Similarly for the circuit of FIG. 1b, the following equation holds true:

1 d 1.' E S11'lwt'C eJ tdt+Rt-l-L t u of Equation 1 represents the velocity of the vibration in the circuit of FIG. 1a, which is equivalent to i of Eqution 2 which represents the electrical current in the circuit of FIG. 1b; w equals 2117, 1 being the frequency of the sinesoidal input signal.

The mechanical impedance, Z of the circuit of FIG.

v1a is as follows:

Similarly, the electrical impedance, Z of the circuit of FIG. 1b is:

A resonant condition is reached where wM equals l/wC for Equation 3, and where wL equals l/wC, for Equation 4. Under such conditions, Z equals R and Z equals R. Such a resonant condition results in a maximum magnitude of u, for the mechanical circuit, and a maximum current, i, for the electrical circuit. At resonance, in both instances, the power factor is unity with force, F being in phase with displacement velocity u, and E voltage being in phase with current, i. It thus can be seen that the resonant condition for the mechanical circuit is closely analogous to that of the electrical circuit.

As the sharpness of resonance of the electrical circuit of FIG. 1b is determined by the Q or figure of merit of the circuit (indicative of the ratio of the energy stored to the energy used in each cycle) which is equal to wL/R; so similarly the sharpness of resonance of Q of the mechanical circuit is as follows:

wM R (5) Mechanical impedance matching operates in the same fashion as electrical impedance matching, with a most efficient transfer of energy occurring where such impedances are properly matched. It can also be shown that the acceleration of a vibrating mass is a function of the square of the frequency of the drive signal. This can be shown as follows:

The instantaneous displacement, y, of a sinesoidally vibrating mass can be represented by the following equation:

Where Y is the maximum displacement in the vibration cycle and w is the angular velocity of such displacement.

The acceleration, a, of the mass can be obtained by differentiating Equation 6 twice, as follows:

The acceleration thus is a function of m which is equal to (21rf) It should be remembered in considering this analysis that the various qualities such as mass, compliance and resistance are seldomly lumped in a mechanical cir cuit, and that most of the elements in such a circuit will exhibit some or all three of these qualities. The schematic representation, thus, is just a convenient way to represent y=Y cos wt the total quantity of each of these qualities that a circuit may have. With this basic analysis in mind, let us now turn to the various figures illustrating the method and devices of the invention.

Referring now to FIGS. 2-4, a first embodiment of the device of the invention suitable for forming strip type workpieces such as moldings and the like is illustrated. Workpiece 12 is held at one end thereof to die member 14 by means of holding clamp 16. The other end of workpiece 12 is attached to piston rod 17 of hydraulic cylinder 20 by means of clamp member 25 which is fixedly attached to the piston rod.

Hydraulic cylinder 20 which provides linear drive means is fixedly attached to stand member 30 by means of bolt 31. When hydraulic cylinder 20 is actuated by forcing fluid through input line 35 to drive piston 37 downwardly, workpiece 12 is drawn in the same direction around the formed end of die member 14 and thereby stretch formed to the shape of the die. Attached to piston rod 17 is orbiting mass oscillator unit 36 which imparts a vibrating force at a sonic frequency to workpiece 12. Orbiting mass oscillator 36 includes a centrally located axle 41 around which a ring shaped rotor 42 is driven by a pneumatic driving force. Oscillators of this type are described in my Patent No. 2,960,314 issued Nov. 15, 1960. An improved embodiment of this oscillator is illustrated in FIGS. 5 and 6 and described further on in this specification.

The eccentric rotation of ring 42 about taxle 41 sets up vibrations in rod 17 which may describe either an elliptical or a circular path depending upon the relative amplitudes of the vibration components thereof. 'I hese vibrations may be resolved into a longitudinal component which vibrationally drives workpiece 12 along its longitudinal axis and a transverse component which excites the workpiece along an axis normal to the longitudinal axis thereof. Oscillator member 36 is operated at a frequency of rotation which produces a resonance with the total effective impedance of a vibrating system, which pri marily includes the workpiece 14, rod 17 and clamp 25 so as to set up standing waves in the workpiece. Such a frequency of rotation is attained by design of the oscillator itself, i.e., for example the choice of the mass of rotor 42, and by proper choice of the velocity of the pneumatic jet stream used to drive the rotor. As explained in the aforementioned Patent No. 2,960,314, the orbiting rotor 42 will tend to synchronously lock in at a rotation speed producing vibrations slightly below the peak reso nant vibration frequency by virtue of the back reaction of the resonantly driven members, and in this fashion optimum operation is automatically achieved. Such resonant lock-in is especially significant in view of the fact that the effective impedance of the driven load and thus the resonant frequency thereof changes somewhat as the workpiece is formed and becomes stiffer. The frequency of oscillation is thus automatically changed with such impedance variations to provide optimum operation at all times. This is a significant feature of this type of oscillator.

Referring to Equation 3, it can be seen that the workpiece is thus vibrated at a frequency slightly below peak resonance, whereby effective compliant reactance,

"co CI.

is slightly greater than mass reactance wM. Under these conditions impedance, Z is substantially equal to mechanical resistance R with the power factor being substantially runity (applied force substantially in phase with the motion). This provides for near optimum efliciency with relatively high amplitude vibrations being produced from a relatively low input signal. Vibrations are set up in workpiece 12 so that standing waves appear therealong. Because the effective impedance of workpiece 12 is generally much lower than that of die member 14, the friction at the interface of these members is markedly reduced so as to desirably ease the flow of the workpiece. This is by virtue of the impedance mismatch between the tWO members resulting in little transfer of energy between the low mass workpiece 12 and high mass die member 14. Thus, workpiece 12 and die member 14 vibrate out of phase with each other and at different amplitudes, and these out-of-phase vibrations tend to ease the motion between the contacting surfaces. This effect is enhanced by virtue of the fact that the other side of the workpiece is in contact only with the atmosphere, which is of very low impedance.

The effectiveness of the sonic action can be implemented by adding auxiliary energy through a supplemental oscillator unit 45 which is fixedly attached to stand member 30. Vibration signals at the resonant frequency of the vibrating members are thus applied to the workpiece at the end thereof held by clamp 16. Such auxiliary excitation is particularly useful in situations where the sonic energy applied by main oscillator 36 tends to die down appreciably before it has reached all the way around to clamp 16.

An additional oscillator 48 may also be used to provide sonic energy to a trouble spot in the forming operation. In this case, energy is delivered from oscillator 48 to a predetermined spot on workpiece 12 through resilient coupling member 54 which may be of rubber. Oscillator 48 and its associated coupling member 50 are urged tightly against workpiece 12 by means of biasing spring 52, so that substantial sonic energy is delivered to the workpiece.

Oscillator units 36, 45 and 48 may all be of similar configuration and are preferably of the type illustrated in FIGS. and 6. Pneumatic drive energy is fed to orbiting mass oscillators 36, 45 and 48 through input lines 56, 57 and 58, respectively. As already noted, simultaneous lateral vibration of the workpiece along with the longitudinal vibration thereof tends to enhance the desired end results. Along these lines, it therefore may be desirable to use pairs of oscillators at any or all of the excitation points, one of such oscillators having its output at the resonant frequency for longitudinal vibration and the other such oscillator having its output at the frequency for lateral resonant vibration.

Referring now to FIGS. 5 and 6, a preferred embodiment of the orbiting mass oscillator unit which may be utilized in the device of the invention is illustrated. The unit illustrated in FIGS. 5 and 6 is an improvement over the devices described in my Patent 2,960,314. This improvement primarily involves the modification of axle member 41 to a hollow configuration with channels 65 being formed in the walls thereof to provide fluid communication to the inner surfaces of rotor 42 which is freely retained within case 60. Thus the pneumatic jet stream for driving the rotor is appliedthrough input line 56 to the hollow center 54 of axle member 41 which is rigidly mounted on case 60. The jet stream flows through channel 65 and tangentially impinges against the inner surface of ring shaped rotor 42. The jet stream thus pro vides the drive force for rotating rotor 42. Air is vented out through ports 66 formed in case 60. It has been found that the drive means of the embodiment of FIGS. 5 and 6 sometimes provides a substantially higher elficiency under the conditions of this combination than does the outer circumference drive described in my aforementioned patent. V

Referring now to FIGS. 7:: and 7b, a second embodiment of the device of the invention is illustrated, in which a punch member is utilized to perform the stretching operation.

In FIG. 7a, punch member 70 is shown in its initial resting position with workpiece 71 lying on stand member 75. When the stem 76 of the punch mechanism is driven downwardly as shown in FIG. 7b, by a suitable drive mechanism (not shown), carn member 77 drives toggles 78 and 79 so that workpiece 71 is firmly clamped at the ends thereof to stand member 75 by means of clamps 80 and 81 attached to the end of the toggles.

Punch member 70 is driven so that it reaches the end of its downward travel in the approximate position indicated in FIG. 7b, so that the center portions of workpiece 71 do not come into contact with stand member '75. Fixedly attached to stem 76 near the end thereof are orbiting mass oscillators 85 and 86, such oscillators preferably being of the type illustrated in FIGS. 5 and 6. The rotor of oscillator 85 rotates about an axis substantially parallel to the longitudinal axis of stem 76 while the rotor of oscillator 86 rotates about an axis substantially normal to the longitudinal axis of stem 76.

As punch member 7%) moves downwardly, it stretch forms workpiece 71 to the desired configuration. While such stretch forming is being accomplished, stem 76 is vibrated along its longitudinal axis as indicated by arrows 88a and 88b, by virtue of the vibrations generated by rotating mass oscillator 86. The rotation frequency of rotating mass oscillator 86 is chosen so that it produces resonance with the effective longitudinal impedance of the punch mechanism which primarily includes stem 76, cam member 77 and punch member 7 0.

Oscillator 85 which rotates to produce vibrations along the axis indicated by arrows 91a and 9111 may be chosen to have a rotation frequency such as to produce a transverse resonant vibration of the punch assembly, this by virtue of resonance with the effective transverse impedance of such assembly. As already noted, oscillators 85 and 86 each tend to lock in at a frequency slightly below the resonant peak frequency of the associated parameter of the punch mechanism.

The resonant vibration of the punch assembly by virtue of the output of orbiting mass oscillator 86 tends to set up standing waves in stem 76 and punch member 70 with motion anti-nodes occurring both in the vicinity of the oscillator and at the interface between punch member '70 and workpiece 71. As clearly shown in Equation 3 such it anti-nodes or peaks are points of minimum impedance. Workpiece 71 is thus excited at a point of maximum magnitude of vibration and minimum impedance with maximum transfer of energy thereto.

It is to be noted that it is essential for proper operation of the device of the invention that the central portion of workpiece 71 not be forced into contact with stand member 75. If such were not the case, the vibration energy would be transferred from relatively high impedance punch member 70 to high impedance stand member 75 with little vibration energy being dissipated in workpiece 71. With the 10W impedance workpiece 71 forming the termination of the mechanical circuit and coupled to the punch member 70 at a matching low impedance point, a maximum amount of sonic energy is transferred to such workpiece to most effectively achieve the desired stress relieving and metal flow characteristics in the shaping ope-ration. The punch mechanism therefore must be adapted so that it does not press workpiece 71 against the die formed in stand 75 as is done in con ventional punch presses.

Additional facilitation of and improvement in the end result of the stretch forming is achieved by virtue of the vibration signals generated by rotating mass oscillator 85, which imparts vibrations to workpiece 71 along an axis substantially normal to the vibrations resulting from the output of oscillator 86. The embodiment of the invention illustrated in FIG. 7a and 7b thus provides means for substantially facilitating and improving the stretch forming of a workpiece with a punch press type mechanism.

In both embodiments of the device of the invention typical sonic vibration frequencies are between 50 and 3000 cycles per second.

The techniques and devices of the invention thus provide simple yet highly effective means for markedly facilitating stretch forming and improving the end results obtainable therewith. The efficient application of sonic energy to the workpiece substantially decreases the amount of tension required for a given amount of bending and makes for a part that can be better formed and which is stress relieved so that it will not go out of shape subsequently due to a later stress relieving influence.

While the techniques and devices of the invention have been described and illustrated in detail, it is to be clearly understood that this is intended by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited solely by the terms of the following claims.

I claim:

1. A method for stretch forming a member in con formance with a forming die comprising the steps of clamping opposite ends of said member to separate holding means,

stretching said member by applying tension thereto,

and

while said member is being stretched applying sonic vibrations thereto, said vibrations being at a resonant frequency for substantially optimum efficiency of transfer ofsonic energy to said member.

2. The method as recited in claim 1 wherein one end of said member is clamped to a forming die and the other end of said member is attached to a pulling device and said member is formed by stretching it around said die.

3. The method as recited in claim 1 wherein the opposite ends of said member are clamped to a stand and said member is stretched by applying pressure to the central portion of one surface thereof with a punch mechanism, the other surfaces of the central portion of said member being kept free from contact with other objects.

4. The method as recited in claim 3 wherein said punch mechanism is vibrated resonantly.

5. The method as recited in claim 1 wherein said member being formed is vibrated resonantly.

6. A method for stretch forming a workpiece comprising clamping one end of said workpiece to a forming die,

drawing the opposite end of said workpiece to stretch said workpiece around said die, and

while said workpiece is being stretched, exciting s-aid workpiece with sonic vibrations at a frequency which causes said workpiece to vibrate resonantly.

7. The method of claim 6 wherein said workpiece is excited by simultaneously applying sonic energy to said opposite end thereof and directly to a broad surface thereof.

8. The method of claim 6 wherein said workpiece is separately excited to cause it to vibrate resonantly along the longitudinal axis thereof and along a transverse axis thereof.

9. A method for stretch forming a workpiece comprising clamping opposite ends of said workpiece to support members, stretching said workpiece by applying pressure to the central portion of one surface thereof with a punch mechanism, the other surfaces of the central portion of said workpiece being kept free from contact with other objects, and while said workpiece is being stretched, applying sonic energy to said punch mechanism at a frequency causing said mechanism to vibrate resonantly,

whereby said workpiece is worked by the vibrations applied thereto to facilitate and improve the forming thereof.

10. The method as recited in claim 9 wherein said punch mechanism is vibrated simultaneously by separate vibration sources at a frequency of substantial resonance wvith the effective longitudinal impedance of said mech- 8 anism and a frequency of substantial resonance with the effective transverse impedance of said mechanism respectively.

11. A device for stretch forming a workpiece comprising means for tightly holding said workpiece at opposite ends thereof,

a form member,

means for stretching the central portion of said workpiece around said form member to assume the shape thereof, and

means for subjecting said workpiece to a resonant vibration frequency, said means including a mechanical oscillator attached to one of said aforementioned means.

12. The device as recited in claim 11 wherein said sonic vibration frequency is substantially the resonant frequency of said workpiece, whereby the compliant reactance of said workpiece is substantially equal to the mass reactance thereof.

13. The device as recited in claim 11 wherein said sonic vibration frequency is substantially the resonant frequency of said stretching means, whereby the compliant react-ance of said stretching means is substantially equal to the mass reactance thereof.

14. A device for stretch forming a workpiece comprising a stand member,

a forming die fixedly supported on said stand member,

means for fixedly clamping one end of said workpiece to said forming die,

linear drive means fixedly mounted on said stand member, said drive means having a drive rod,

means for clamping the end of said workpiece opposite said one end thereof to the drive rod of said drive means, and

mechanical oscillator means fixedly mounted on said drive rod, said oscillator means having an output frequency which is substantially the frequency of resonance of the combined effective impedance of said rod and said workpiece.

15. The device as recited in claim 14 and additionally including second mechanical oscillator means having substantially the same output frequency as said first oscillator means, said second oscillator means being mounted on said stand member.

16. The device as recited in claim 14 and additionally including second mechanical oscillator means having substantially the same output frequency as said first oscillator means, said second oscillator means being mounted to directly drive a predetermined portion of said workpiece.

17. A device for stretch forming a workpiece comprising a stand member,

means for clamping the opposite ends of said workpiece to said stand member,

a punch assembly including punch member means for forming said workpiece, said punch assembly being adapted to cause said punch member to stretch the central portion of said workpiece without causing said central portion to be driven against other objects, and

mechanical oscillator means mounted on said punch assembly for resonantly vibrating said punch assembly,

whereby sonic energy is efficiently transferred to said workpiece to facilitate and improve the forming thereof.

18. The device as recited in claim 17 wherein said mechanical oscillator means includes a first mechanical oscillator mounted to vibrate said punch assembly along a longitudinal axis thereof and a second mechanical oscillator mounted to vibrate said punch assembly along a transverse axis thereof, said first oscillator having an output frequency resonant with the effective longitudinal impedance of said punch assembly, said second oscillator having an output frequency resonant with the effective transverse impedance of said punch assembly.

19. A device for stretch forming a workpiece comprising a stand member, a forming die fixedly supported on said stand member, means for fixedly clamping one end of said workpiece to said forming die, means fixedly mounted on said stand member and attached to the end of said workpiece opposite said one end thereof for drawing said workpiece around said die, and mechanical oscillator means for resonantly vibrating said workpiece at a sonic frequency while it is being drawn around said die. 20. The device as recited in claim 19 wherein said mechanical oscillator is attached to said drawing means. 5 21. The device as recited in claim 19 wherein said drawing means includes a hydraulic cylinder having a drive rod, said drive rod being attached to said end of said workpiece opposite said one end thereof.

References Cited UNITED STATES PATENTS 2,995,050 8/1961 Karron et a1 72-205 CHARLES W. LANHAM, Primary Examiner.

15 R. D. GREFE, Assistant Examiner. 

1. A METHOD FOR STRETCH FORMING A MEMBER IN CONFORMANCE WITH A FORMING DIE COMPRISING THE STEPS OF CLAMPING OPPOSITE ENDS OF SAID MEMBER TO SEPARATE HOLDING MEANS, STRETCHING SAID MEMBER BY APPLYING TENSION THERETO, AND WHILE SAID MEMBER IS BEING STRETCHED APPLYING SONIC VIBRATIONS THERETO, SAID VIBRATIONS BEING AT A RESONANT FREQUENCY FOR SUBSTANTIALLY OPTIMUM EFFICIENCY OF TRANSFER OF SONIC ENERGY TO SAID MEMBER. 